Input: atmel_mxt_ts - fix merge in DT documentation

Something went a bit wrong in merging f5940231a - there's a bit of repeated
text that's been introduced.

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/atmel,maxtouch.txt

@@ -11,10 +11,6 @@ Required properties:
 
 Optional properties for main touchpad device:
 
-- linux,gpio-keymap: An array of up to 4 entries indicating the Linux
-    keycode generated by each GPIO. Linux keycodes are defined in
-    <dt-bindings/input/input.h>.
-
 - linux,gpio-keymap: When enabled, the SPT_GPIOPWN_T19 object sends messages
     on GPIO bit changes. An array of up to 8 entries can be provided
     indicating the Linux keycode mapped to each bit of the status byte,